Molecular mobility of polypeptides containing proline as determined by 13 C magnetic resonance

The molecular conformations and dynamics of poly( L ‐prolyl), poly(hydroxyl‐ L ‐prolyl), poly( L ‐prolyl‐glycyl), poly(hydroxyl‐ L ‐prolyl), and poly(glycyl‐glycyl‐ L ‐prolyl‐glycyl), in aqueous solution, have been studied using 13 C pulse Fourier transform nmr spectroscopy. From a measurement of the intensities of major and minor resonances in the spectra of the copolypeptides, it was determined that 15–20% of the glycyl‐prolyl and glycyl‐hydroxyprolyl peptide bonds are cis. Effective rotational correlation times (τ eff ), obtained from measurements of spin‐lattice relaxation times ( T 1 ) of individual backbone and side‐chain carbons, demonstrated that backbone reorientation is approximately isotropic for the five polypeptides and is characterized by correlation times of ca. 0.3–0.6 nanoseconds as a result of rapid segmental motion. In a given polypeptide glycyl and pyrrolidine residues were found to have the same backbone correlation times, but backbone carbon τ eff values did decrease as the glycyl content of the peptides increased. A semi‐quantitative analysis of C β , C γ , and C δ correlation times suggests that rapid ring motion in both prolyl and hydroxyprolyl involves primarily C γ and C β , with the prolyl ring being more mobile than the hydroxyprolyl ring.